Human Prion Diseases
by André Delacourte and Clive Evers
Group of rare and fatal brain disorders called the prion diseases. These occur in both humans and animals and designed as spongiform encephalopathies. All subgroups, sporadic or familial, result from a defect of a protein named prion, which aggregates in the nervous tissue and provokes a rapid neurodegeneration.
Clinical subgroups are :
- Sporadic CJD
- Transmissible CJD
- Iatrogenic CJD
- New variant form of CJD
- Familial CJD
- Gerstmann-Straussler-Scheinker disease (GSS)
Symptoms and course
Prion diseases cause a progressive but generally rapid loss of mental abilities and is accompanied by neurological symptoms such as unsteadiness and clumsiness.
All forms have generally an early onset, between 20 to 50 years. The evolution is generally between 12 to 60 months.
Causes and risk factors
Prion diseases are transmissible in certain circumstances, but they are not infectious in the usual way. So they are not spread by airborne droplets, blood or sexual contact.
Contact with someone with CJD does not lead to increased risk of developing the conditions no special precautions are required.
The infectious agent is thought to be a prion, an abnormal form of a protein called PrP, which in its natural form occurs in the brain and parts of the body of humans.
Unlike bacteria and viruses, prions are not inactivated by heat, ultraviolet light or other standard sterilisation procedures. Normal Prp can convert into abnormal PrP, named PrPres, which leads to disease.
In general, EEG and MRI analysis are used to demonstrate an atrophy and the lack of other causes such as vascular pathology, genetic analysis of the prion gene, analysis of biological markers in the CSF, post-mortem examination of prion amyloid plaques help to diagnose and to type the different prion pathologies.
Clear, accurate information about the disease is necessary, as there is still many stigmas attached to CJD. Prompt, coordinated multidisciplinary support for the patient and their family is important.
Social services should be involved early on to advise on financial benefits, day care, respite care and long-term care.
Although there is no evidence that CJD can be transmitted through blood, people with a history of CJD are asked not to give blood to minimise any potential risk.
Carers will need help from speech and occupational therapists and district nurses may provide general nursing care and advice. Carers may find that the person with CJD will behave in an aggressive way, which is uncharacteristic of their usual personality. It is important to try to identify any triggers for aggression and takes steps for prevention.
Keeping a diary may help to identify the pattern of events. The brain damage caused by prion disease can sometimes cause swallowing problems, which are distressing for the person with CJD and their carers. These problems may also lead to malnutrition if eating/swallowing become difficult. It is important to ask for a referral to a speech and language therapist for advice.
Ongoing research/Clinical trials
New clinical approaches in development, such as vaccination or anti-aggregation drugs (beta-sheet breakers). Prof. Stanley Prusiner, California, USA, published a paper in the Proceedings of the National Academy of Science 14 August 2001 suggesting potential treatments. The research gave evidence of stopping the formation of the disease associated form of prion protein in scrapie (prion disease in sheep) infected cells by a number of compounds with quinacrine and chlorpromazine showing the greatest potency.
These drugs have been used in humans for many years as anti-malarial and anti-psychotic drugs and Prof. Prusiner suggested that they are immediate candidates for treatment of CJD and other prion diseases.
Clinical trials of these drugs are however needed and they are currently being planned. During 2002 there has been some publicity about the possible application of pentosan polysulphate for CJD. There is evidence of at least one person with CJD being administered with it. This is widely used in North America for the treatment of interstitial cystitis. It is unlicensed in the United Kingdom.
Care and treatment
There is no treatment at present for CJD. However, there are a number of drugs, which can relieve the symptoms and make the patient more comfortable.
These include valproate and Clonazepam for jerking movements. The patient and their carers will also need much help from social services and nursing services.
Last Updated: vendredi 09 octobre 2009